Medical treatment of many illnesses requires continuous drug infusion into various parts of the body via subcutaneous and/or intravenous injections. Diabetes mellitus patients, for example, require the administration of varying amounts of insulin throughout the day to control their blood glucose levels. In recent years, ambulatory portable insulin infusion pumps have emerged as a superior alternative to multiple daily syringe injections of insulin for Type 1 and Type 2 diabetes patients. These pumps, which deliver insulin at a continuous basal rate, as well as in bolus volumes, were developed to liberate patients from repeated self-administered injections, and allow them to maintain a near-normal daily routine. Both basal and bolus volumes must be delivered in precise doses, according to individual prescription, since an overdose or underdose of insulin could be fatal.
The first generation of portable insulin pumps refers to a “pager-like” device with a reservoir contained within a housing. The reservoir is typically a barrel-shaped, syringe-like component which enables the delivery of medicine by a continuous forward motion of a plunger into the reservoir. Examples of such devices are disclosed in U.S. Pat. Nos. 6,248,093 and 7,390,314. In conventional configurations, a motor rotates a gear, which in turn rotates a threaded drive screw. The plunger has a proximal end that contains gaskets and an elongated member shaped like a cylinder which is internally threaded for engagement with the drive screw. As a result, the motor rotates the drive screw which engages the threads of the cylinder and converts the rotation of the drive screw into a linear motion to displace the plunger in an axial direction. These first generation devices represent a significant improvement over multiple daily injections, but suffer major drawbacks, including large size, heavy weight, and long tubing.
To avoid these drawbacks, a new concept was proposed and implemented in second generation pumps. The new concept concerns a remote-controlled, skin-adherable device having a bottom surface adapted to be in contact with a patient's skin. A reservoir is contained within the housing and filled using an additional syringe to draw medicine from a vial with an injection needle into the reservoir. This concept is discussed in U.S. Pat. Nos. 4,498,843, 5,957,895, 6,589,229, 6,740,059, 6,723,072, and 6,485,461. These second generation devices still have several drawbacks, the most significant being that the entire device should be disposed every 2-3 days (due to insertion site infections and reduced insulin absorption), including all the expensive components, such as electronics and the driving mechanism.
A typical driving mechanism of a second generation device is described in U.S. Patent Application Publ. No. 2005/0238507 assigned to Insulet Corporation. In this device, a plunger is rigidly connected to a non-rotating threaded drive screw and also coupled to a drive wheel that includes a thread-engaging mechanism that moves from a non-thread-engaging position to a thread-engaging position. The non-thread-engaging position allows the threaded drive screw to pass freely through the drive wheel when the reservoir is being filled. The thread-engaging position allows the threaded drive screw to be advanced when the drive wheel is rotated.
A third generation of pumps was devised to avoid the cost issues associated with second generation pumps and to expand patient customization. Examples of such devices are described in co-owned, co-pending U.S. patent application Ser. No. 11/397,115 (Publication No. 2007/0106218), filed on Apr. 3, 2006 and entitled “Systems and Methods for Sustained Medical Infusion and Devices Related Thereto,” and co-owned International Patent Application No. PCT/IL06/001276 (Publication No. WO/2007/052277), filed on Nov. 5, 2006 and entitled “Modular Portable Infusion Pump,” the disclosures of, which are incorporated herein by reference in their entireties. These third generation devices contain a remote control unit and a skin-securable (e.g., adherable) dispensing unit having two parts: (1) a reusable part containing electronics, at least a portion of the driving mechanism and other relatively expensive components, and (2) a disposable part containing the reservoir and other less expensive components. Other third generation devices are also disclosed in co-owned, co-pending U.S. patent application Ser. No. 11/989,681, filed on Jan. 28, 2008, and co-owned International Patent Application No. PCT/IL07/000932 (Publication No. WO/2008/012817), filed on Jul. 24, 2007, both entitled “Systems, Devices, and Methods for Fluid/Drug Delivery,” the disclosures of which are incorporated herein by reference in their entireties.
A typical driving mechanism of third generation devices is described in U.S. Patent Application Publ. No. 2008/0097327 assigned to Medtronic MiniMed. This device has a disposable part that includes a plunger having a rigidly-connected drive screw. The device also has a reusable part that contains a motor and a gear that comprises a drive wheel. Upon connection of the reusable part and disposable part, the drive screw is engaged with the drive wheel. Rotation of the drive wheel is converted to linear motion of the drive screw.
A fourth generation of pumps was devised as dispensing units that can be disconnected and reconnected to a skin-securable (e.g., adherable) cradle unit and can also be operated by buttons located on the reusable part. Examples of fourth generation devices are disclosed in co-owned, co-pending U.S. patent application Ser. No. 12/004,837 (Publication No. 2008/0215035) and co-owned International Patent Application No. PCT/IL07/001578 (Publication No. WO2008/078318), both filed on Dec. 20, 2007 and entitled “Systems, Devices, and Methods for Sustained Delivery of a Therapeutic Fluid,” the disclosures of which are incorporated herein by reference in their entireties. Other fourth generation devices are also disclosed in co-owned, co-pending International Patent Application No. PCT/IL08/001001 (Publication No. WO2008/078318), filed on Jul. 20, 2008 and entitled “Manually Operable Portable Infusion Pump,” and co-owned, co-pending International Patent Application No. PCT/IL08/001057 (Publication No. WO2009/016636), filed on Jul. 31, 2008 and entitled “Portable Infusion Device Provided with Means for Monitoring and Controlling Fluid Delivery,” the disclosures of which are incorporated herein by reference in their entireties.
Third and fourth generation devices may be incorporated with an analyte (e.g., glucose) sensing apparatus that enables continuous readings of analyte levels. Based on these analyte readings, fluid may then be automatically (i.e., a closed-loop system) dispensed or semi-automatically (i.e., an open-loop system) dispensed, should the user wish to control delivery. Fourth generation sensing and dispensing devices are disclosed in co-owned, co-pending U.S. patent application Ser. No. 11/706,606 (Publication No. 2007/0191702), filed on Feb. 14, 2007 and entitled “Systems and Methods for Sensing Analyte and Dispensing Therapeutic Fluid,” in co-owned, co-pending U.S. patent application Ser. No. 11/963,481 (Publication No. 2008/0214916), filed on Dec. 21, 2007 and entitled “Fluid Delivery with In Vivo Electrochemical Analyte Sensing,” and in co-owned International Patent Application No. PCT/IL2007/001579 (Publication No. WO2008/078319), filed on Dec. 20, 2007 and entitled “Fluid Delivery with In Vivo Electrochemical Analyte Sensing,” the disclosures of all of which are incorporated herein by reference in their entireties.
Third and fourth generation devices may also be two-part (e.g., a disposable part and a reusable part) skin-securable (e.g., adherable) devices having a “syringe-type” pumping mechanism. Here, a plunger slides within the reservoir to urge fluid (e.g., insulin) out of the reservoir. The plunger may be moved forward by a rotating drive screw that has a distal end coupled with the plunger. Linear motion may be achieved by rotation of the drive screw within a non-rotating drive nut disposed in the disposable part of the device. Rotation of the drive screw within the non-rotating drive nut causes linear motion of the drive screw relative to the drive nut. In such devices, the drive screw may also be used as a handle for pulling the plunger out of the reservoir for reservoir filling. After filling, the disposable part is connected to the reusable part, thereby engaging the drive screw with the driving mechanism in the reusable part of the device.
One major limitation of this design concerns the misalignment and/or eccentricity of the drive screw during the forward motion of the plunger within the reservoir. In particular, manufacturing and/or assembly tolerances of the driving mechanism may result in eccentric rotation of the drive screw within the device and/or the engagement of the proximal end of the drive screw with the driving mechanism may become misaligned and cause such eccentric rotation of the drive screw. This eccentric rotation of the drive screw is transferred to the plunger during the plunger's forward motion within the reservoir and creates plunger wobbling within the reservoir. This wobbling results in mechanical inefficiencies within the device and causes inaccuracies in the amount and rate of fluid delivery to the body.